Impulsive rocket motor safety-arming device

ABSTRACT

An impulsive safety-arming device provides handling safety in a rocket  mo. Prior to arming, a piston is blocked in position to contain a squib, thereby preventing inadvertent ignition. After arming, the piston block is removed allowing high temperature, high pressure gas from the squib to force the piston past vent ports and to escape and ignite the motor.

BACKGROUND OF THE INVENTION

This invention relates to safety-arming devices for rocket motorswherein an electro-initiator device (EID) is used to ignite a boostercharge of pyrotechnic material which in turn ignites the rocketpropellant. More particularly, this invention relates to such deviceswhich will prevent rocket motor ignition by containing premature EIDcombustion, and which utilize energy from the properly ignited EID toremove an ignition barrier between the EID and the booster charge.

Rocket motors of the type used in guided missiles which are launchedfrom surface or airborne platforms use a variety of devices forpreventing unintentional rocket motor ignition. One class of suchdevices uses an EID aligned with a booster charge in the rocket motorand rendered safe by electric switches, electronic filters, electricallyinsensitive bridgewires or by a combination of such elements. Anotherclass of similar devices utilizes a barrier between the EID and thebooster charge. When rocket motor ignition is likely to be desired, thebarrier is removed manually by external means.

These designs are not sufficiently fail-safe to be stored in quantity inthe assembled condition and thus must have the EID installed just priorto use. Also it is possible for inexperienced personnel to improperlyarm the rockets thereby making them impossible to launch, or tounintentionally store rockets in the armed condition with other unarmedrockets and thus create an unreasonable danger of explosion. Further,freedom of missile design is somewhat restricted if a provision must bemade for installation of an EID prior to use. The missile must have anaccess port for EID installation and therefore will result in a morecomplex structure than if the EID is permanently installed deep withinthe missile.

SUMMARY OF THE INVENTION

The safety-arming device of the present invention uses a sealed pistonsliding within a vented outer housing. An electrically initiated squibdevice (EID) is placed within the piston and is sealed against leakageso that when the squib is ignited, it produces a large quantity of hightemperature, high pressure gas which drives the piston to the oppositeend of the outer housing. The EID, piston and seal remain intact afterignition to prevent leakage so that the gas pressure may act on thepiston rather than escape through the piston to the interior of thesafety-arming device. The piston uncovers a plurality of vents as ittravels. High temperature, high pressure gas confined within the housingby the piston escapes through the uncovered vents and ignites apyrotechnic booster charge which ignites the rocket motor propellant.

A mechanical blocking member is positioned to forcibly retain the pistonin its initial position covering all housing vents. This blocking memberhas sufficient strength to withstand the force on the piston caused bygas pressure from the squib if the squib is ignited unintentionally orprematurely.

A step motor aligned axially with the blocking member rotates theblocking member ninety degrees from a safety position in which pistontravel is prevented, to an armed position in which piston travel ispossible. This motor is controlled by externally generated signals whichprecede an intentional launch.

If the squib is ignited when the blocking member is in the safetyposition the high pressure gas produced by the squib is contained by theouter housing and piston, and ignition of the rocket motor is prevented.An added safeguard against premature or unintentional rocket motorignition is the electric current supply circuit to the squib. Thiscircuit employs electrical contacts which are only closed when theblocking member is rotated to the armed position.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the present invention will emerge from adescription which follows of a possible embodiment of a safety-armingdevice according to the invention, given with reference to theaccompanying drawings, in which:

FIG. 1 is a longitudinal sectional view of a safety-arming device in thesafety position;

FIG. 2 is a perspective exploded view of the blocking member and pistonbase according to the invention;

FIG. 3 is a partially cut away sectional view of the invention within arocket motor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings wherein like reference numerals correspondto like parts and elements throughout the several figures there is shownin FIG. 1 elongated cylindrical housing 11 equipped with a plurality ofvent ports 12. Within housing 11 resides hollow piston 13 and pistonbase 55. Piston 13 is sealed against the inner surface of housing 11 inhousing cavity 16 by resilient o-rings 14 which encircle piston 13.O-rings 14 are separated by resilient separator 15. Hollow piston 13 hasa centrally bored stepped hole 71 which retains electro-initiator squib21 against threaded end 72 of piston base 55. Electrical lead-in wires22 and 23 from squib 21 lead through central cavity 73 of piston base 55and are firmly attached to electrical contacts 24 and 25 on piston baseisolation member 32. Elongated cylindrical housing 11 is firmly attachedto main housing 51 by any appropriate means. FIG. 1 illustrateselongated cylindrical housing 11 being threaded into main housing 51,but it is to be understood that other fastening means will work as well.Piston base isolation member 32 is retained to piston base 55 by beingcemented to piston base flange 31. Piston base isolation member 32 hasprojections 33, 33' which penetrate piston base flange 31 and engageshallow holes 75, 75' in housing 51, thereby preventing relativerotation between piston base isolation member 32 and main housing 51.

Within main housing 51 is contained stationary blocking member 41 whichis rigidly retained within housing 51 and braced against relativerotation by pins 45, 45' as shown in FIG. 2, which project into holes inmain housing 51. Within stationary blocking member 41 is rotationalblocking member 36 which is free to rotate through a predeterminedangular displacement within central bore 76 of stationary blockingmember 41. Rotational blocking member 36 has central receiving cavity 35shown in FIG. 1 positioned ninety degrees to the longitudinal directionof piston base isolation member 32. This relative orientationcorresponds to the safety-arming device being in the safety position.Rotational blocking member 36 is retained within stationary blockingmember 41 by ears 53, 53' which abut sliding surfaces 47, 47' onstationary blocking member 41. Recesses 48, 48' in the side ofstationary blocking member 41 provide room for ears 53, 53' to enterwhen piston base 55 and piston base isolation member 32 are forced bygas pressure in housing cavity 16 to enter central receiving cavity 35in rotational blocking member 36.

When rotational blocking member 36 has been rotated to the armedposition by shaft 39 which is powered by electric motor 81, in responseto a first externally generated signal, piston base isolation member 32no longer bears against blocking surfaces 34, 34' and is able to entercentral receiving cavity 35. When squib 21 is ignited, piston baseisolation member 32 bottoms in receiving cavity 35 and forces rotationalblocking member 36 forward on splines 37 of shaft 39. Rotationalblocking member 36 disengages splines 37 and frees shaft 39 for otherfunctions. Splines 37 then enter enlarged hole 38.

Rotational blocking member 36 is also restrained by a supporting member,not shown, which bears against tang 54 on rotational blocking member 36and prevents axial motion when rotational blocking member 36 is in thesafety position. This supporting member allows axial motion only whenrotational blocking member 36 is rotated to the armed position, therebyaligning tang 54 with a receiving cavity, not shown, in the supportingmember. This supporting member is rigidly attached to housing 51 andoccupies space adjacent blocking members 36 and 41 in the region forwardof central bore 76.

Torsional coil spring 42 engages both stationary and rotational blockingmembers 41 and 36 and produces a relative torque which urges ear contactsurfaces 52, 52' against stop contact surfaces 46, 46' on stationaryblocking member 41 thereby yieldingly retaining rotational blockingmember 36 in the safety position.

Stationary blocking member 41 has electrodes 26 and 27 embedded in stops65, 65' which are supplied with electric current by lead-in wires 28 and29. Lead-in wires 28 and 29 follow lead-in paths 43 and 44 to electrodes26 and 27. As shown in FIG. 1, electrodes 26 and 27 are positionedadjacent electrical contacts 24 and 25 on piston base isolation member32. Electrical contact bridging members 49, 49' on ears 53, 53'electrically bridge between electrodes 26 and 27, and electricalcontacts 24 and 25, respectively when rotational blocking member 36 isrotated to the armed position. When rotational blocking member 36 isrotated to the safety position electrical contact bridging members 49,49' are separated from electrodes 26 and 27 and electrical contacts 24and 25 so that no continuity exists in the circuit supplying firingenergy to electro-initiator squib 21.

Piston base 55 and piston 13 are connected by screw threads at 72 toallow disassembly so that piston base 55 may be inserted through mainhousing 51 at close fitting hole 19. During the assembly process, pistonbase 55 is cemented to piston 13 over the area of threads at 72 with anepoxy sealant to prevent piston base 55 from disengaging piston 13 andalso to prevent possible gas leakage past the threaded area at 72.

Main housing 51 and attached elongated cylindrical housing 11, togethermaking up safety-arming assembly 10, are installed in missile 61 nearthe head end of combustion chamber 62 as shown in FIG. 3. In normaloperation within a missile, when missile launch is desired, rotationalblocking member 36 is rotated to the armed position and squib 21 iselectrically ignited. Gas pressure in housing cavity 16 presses againstpiston 13 and forces piston base 55 into central receiving cavity 35 inrotational blocking member 36. At this time shoulder 17 moves throughspace 74 and compresses o-ring 18 against main housing shoulder 76. Gasescaping from vent ports 12 ignites pyrotechnic material in canister 64and in a very short period of time completely fills combustion chamber62 with a high temperature high pressure gas which uniformly ignites theexposed surfaces of solid propellant 63. As pressure in combustionchamber 62 increases, piston 13 at shoulder 17 compresses o-ring 18 withstill greater force thereby producing an even tighter obturating seal.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:
 1. An impulsive safety-arming device for preventingunintentional ignition of a rocket motor, comprising:a housing defininga plurality of vent ports; a piston retained within said housing andconstrained to motion between first and second piston positions;resilient sealing means retained between said piston and said housing;said piston, housing, and resilient sealing means defining a confinedvolume characterized by said piston being in said first piston position;said resilient sealing means being positioned to enable fluidcommunication between said confined volume and said vent ports when saidpiston is in said second piston position; piston blocking meanspositionable to forcibly retain said piston in said first pistonposition, retained within said housing; means for moving said pistonblocking means from said retaining position, said moving means engagingsaid piston blocking means and being responsive to a first externallygenerated signal; and means for generating fluid pressure within saidconfined volume, said fluid pressure generation means being responsiveto a second externally generated signal.
 2. The impulsive safety-armingdevice of claim 1 wherein:said housing is an elongated right circularcylinder having two ends and a central bore closed at one end, and saidplurality of vent ports are spaced from said closed end and communicatebetween said central bore and the exterior of said cylinder; and saidpiston is a cylindrical tube having first and second ends, a narrowrecess formed circumferentially about said piston at said first end, andadapted to sealingly retain an electrically initiated squib within saidtube.
 3. The impulsive safety-arming device of claim 2 in combinationwith a canister containing a pyrotechnic material, both securely mountedwithin a rocket motor combustion chamber, and said safety-arming devicebeing retained in intimate contact with said pyrotechnic material. 4.The impulsive safety-arming device of claim 2 in combination with acanister containing a pyrotechnic material, both said device and saidcanister being securely mounted within a rocket motor combustionchamber, and said safety-arming device being retained in intimatecontact with said pyrotechnic material.
 5. The impulsive safety-armingdevice of claim 4 wherein said piston has an elongated region of reduceddiameter bounded by shoulders of increased diameter, said region spacedfrom said narrow recess, and said region penetrating a like diameterhole in said housing, said piston being constrained thereby to movebetween said first and second piston positions.
 6. The impulsivesafety-arming device of claim 5 wherein an elastic ring encircles saidpiston in said region of reduced diameter and forms a gas tightobturating seal between said housing an one of said shoulders on saidpiston when said piston is in said second piston position.
 7. Animpulsive safety-arming device for enabling safe storage and handling ofa rocket motor, comprising:a housing defining a plurality of vent ports;a piston sealingly retained within said housing and constrained tomotion between first and second piston positions; said piston andhousing defining a confined volume characterized by said piston being insaid first piston position; said plurality of vent ports beingpositioned to enable fluid communication between said confined volume,and the exterior of said housing when said piston is in said secondpiston position; piston blocking means retained within said housing andmovable between first and second blocking positions for forciblyretaining said piston in said first piston position when said pistonblocking means are in said first blocking position; means engaging saidpiston blocking means for moving said piston blocking means from saidfirst blocking position to said second blocking position in response toa first externally generated signal; and means associated with saidconfined volume for generating fluid pressure within said confinedvolume in response to a second externally generated signal.
 8. Theimpulsive safety-arming device of claim 7 wherein said fluid pressuregenerating means comprises an electrically initiated gas generatingsquib.
 9. The impulsive safety-arming device of claim 8 whereinelectrical contact means are attached to and cooperate with said pistonblocking means and said piston for establishing a continuous electricalcircuit between an external signal source and said electricallyinitiated squib when said piston blocking means is in said secondblocking position.
 10. The impulsive safety-arming device of claim 9wherein said piston blocking means has inner and outer members:saidouter member having a central bore, first and second ends, said firstend defining a plurality of stops, and having at least one electrodeforming part of an electrical contact at said first end, said outermember being rigidly attached to said housing; and said inner membercoextensively occupying said central bore in said outer member, havingprojections which constrain said inner member to limited angularrotation between first and second rotational positions and tolongitudinal travel only at preselected relative rotational positions bycontacting said plurality of stops on said outer member, and havingbridging electrodes on said projections for completing electricalcontinuity from said electrode on said outer member to said electricalcontact means on said piston; said inner member also having a cavity ofreceiving said piston when said inner member is in said secondrotational position, and a blocking surface adjacent said receivingcavity for forcibly retaining said piston in said first piston positionwhen said inner member is in said first rotational position, and whereinsaid piston blocking means has resilient means for urging projections onsaid inner member rotatably against said stops on said outer member,said inner member being yieldingly retained thereby in said firstrotational position.
 11. The impulsive safety-arming device of claim 10wherein:said inner member has a centrally located splined hole foraccepting a splined shaft, and said means for moving said pistonblocking means is an electric motor having a splined shaft engaging saidsplined hole in said inner member for rotating said inner member fromsaid first rotational position to said second rotational position inresponse to said first externally generated signal.
 12. An impulsivesafety-arming device for enabling safe storage and handling as well asfor providing reliable ignition of a rocket motor, comprising:a gasgenerator; a container surrounding said gas generator for containing gasproduced by said gas generator; and condition responsive meansassociated with said container for causing said container to fail tocontain said gas in response to predetermined conditions.
 13. Animpulsive safety-arming device as set forth in claim 12 wherein said gasgenerator comprises an electrically initiated squib.
 14. An impulsivesafety-arming device as set forth in claim 12 wherein said predeterminedconditions include reception by said condition responsive means of afirst externally generated signal.
 15. An impulsive safety-arming deviceas set forth in claim 12 wherein said container comprises:a housing; apiston sealingly retained within said housing and movable between firstand second piston positions; and piston blocking means associated withsaid housing and movable between first and second blocking positions.16. An impulsive safety-arming device as set forth in claim 15 whereinsaid condition responsive means comprises:said housing having aplurality of vent ports; said piston and housing defining a confinedvolume characterized by said piston being in said first piston position;said piston being blocked in said first position by said piston blockingmeans being in said first blocking position, and said piston beingunblocked by said piston blocking means being in said second blockingposition; and means associated with said housing for moving said pistonblocking means from said first blocking position to said second blockingposition.